Allen J. Schaben of the Los Angeles Times took this picture of the whale skeleton

A construction crew was digging a hole for a storm-water runoff tank at the San Diego Zoo, when the excavator suddenly hit something in the dirt that made a scraping sound.

It turns out there was a fossilized 3 million-year-old whale skeleton under all the living animals at the zoo.

When the skeleton was uncovered, a paleontologist from the San Diego Natural History Museum was already at the construction site, acting as a sort of “fossil monitor”. Often, big construction projects with a lot of excavation are required to have a paleontologist check the site to make sure historical artifacts aren’t being destroyed by digging.

The paleontologist heard the sound and the digging stopped. California state law requires that construction be halted when something of fossil, or archeological, interest is uncovered. This is to give experts time to examine the site and make arrangements to preserve and move their findings.

More paleontologists from the museum were called, and within a day, the group was carefully chipping, dusting, and digging. The skeleton will be encased in plaster at the site and taken back to the museum for additional study.

Meanwhile, work on the storm-water project resumed.

Paleontologists had expected that digging at the site might uncover some minor fossils. But finding a whole fossilized whale , particularly one 20 feet long and largely intact, was unexpected.